Japanese Patent Laying-Open No. 2005-237149 discloses a power supply device for a vehicle. This power supply device for a vehicle includes a battery, an up-converter, and a starter unit to start an engine. The battery, up-converter, and starter unit are connected to a power supply line through which a power supply voltage of an electric load is supplied.
When the up-converter is inactive, the output voltage of the battery is supplied to the power supply line. When the up-converter is active, the voltage boosted by the up-converter is supplied to the power supply line. The up-converter operates intermittently in accordance with the operating period of the starter unit. Specifically, the voltage supplied to the starter unit is boosted by the up-converter in this power supply device for a vehicle when the engine is started by the starter unit.
When the up-converter is operated, the loss at the up-converter as well as the loss at the inverter directed to driving the starter motor will be increased. Therefore, in the case where the temperature is extremely low such that the battery output is significantly reduced and the cranking resistance of the engine is increased, for example, the power to drive the starter motor at the time of engine startup may be so low that there is a possibility of not being able to start the engine.